Manganese complexes containing the ligands Me3-TACN (1,4,7-trimethyl-1,4,7-triazacyclononane) and Me4-DTNE (1,2-bis-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)-ethane) are of interest for different bleaching of cellulosic and other substrates.
Different methods have been disclosed to synthesise 1,4-ditosyl-1,4,7-triazacyclononane (Ts2-TACN) from 1,4,7-tritosyl-1,4,7-triazacyclononane (Ts3-TACN) as described below.
Ts3-TACN has been treated with a mixture of bromic acid and acetic acid for 20 h at 100° C. and subsequently refluxed for 30 h to yield fully detosylated 1,4,7-triazacyclononane (H3-TACN) as HBr salt, i.e. H3-TACN.HBr; subsequent reaction with 2 equivalents of tosyl chloride afforded Ts2-TACN in 60% yield as disclosed in Inorg. Chem., 1985, 24, 1230.
Ts3-TACN has been treated with a mixture of bromic acid, acetic acid and phenol for 36 h at 90° C., to furnish monotosylated Ts-TACN. Further reaction with 1 equivalent of tosyl chloride to afford Ts2-TACN in a higher yield than using method 1-76% as disclosed in Inorg. Chem., 1990, 29, 4143.
Ts3-TACN has been heated with a mixture of hydrobromic acid and acetic acid under reflux for 3 h to yield a mixture of Ts-TACN.HBr (68%) and Ts2-TACN.HBr(30%) as disclosed in Synthetic Communications, 2001, 31(20), 3141.
Isolation of protonated Ts2-TACN salt with bromide as counter ion has been described in Synthetic Communications 31(20), 3141-3144, 2001; and US 2005/112066 A1.
The reaction of Ts2-TACN with 2 equivalents of ditosyl-ethyleneglycol in DMF to yield 1,2-bis(4,7-ditosyl-1,4,7-triazacyclonon-1-yl)-ethane (Ts4-DTNE) is also disclosed in Inorg. Chem. 1985, 24, 1230; Inorg. Chem. 1996, 35, 1974-1979; Inorg. Chem. 1998, 37(5), 3705-3713; Inorg. Chem. 2005, 44 (2), 401-409; and J. Chem. Soc., Dalton Trans. 1994, 457-464.
Ts4-DTNE has also been obtained using O,O′,N,N′-tetratosyl-N,N′-bis(2-hydroxyethylethylenediamine and ethylenediamine (Synthesis 2001, 2381-2383; Inorg. Chem. 2007, 46(1), 238-250; Green Chem. 2007, 9, 996-1007).
Synthesis of 1,2-bis(1,4,7-triazacyclonon-1-yl)-ethane (DTNE) from methine-1,4,7-triazacyclononane and dibromoethane or diiodoethane has been disclosed in J. Chem. Soc., Chem. Commun., 1987, 886; J. Am. Chem. Soc., 1998, 120, 13104-13120; Inorg. Chem. 1993, 32, 4300-4305; Inorg. Chem. 1997, 36, 3125-3132; Chem. Lett. 2000, 416-417; J. Chem. Soc., Dalton Trans., 2000, 3034-3040.
Synthesis of Me4-DTNE from DTNE using formaldehyde and formic acid can be found in J. Am. Chem. Soc., 1998, 120, 13104-13120; Inorg. Chem. 1993, 32(20), 4300-4305; Chem. Lett., 2000, 416-7.
Using the known methods, the binucleating triazacyclononane ligand can be obtained in a reasonable yield. However, as the purity level is insufficient to obtain the dinuclear manganese complex ([MnIVMnIII (μ-O)2(μ-OAc)(Me4-DTNE)]2+) in high yield, an additional purification step, such as vacuum destillation is needed. Although this gives then a high purity material, the yield loss is quite substantial. Therefore there is still a need to be able to synthesise manganese complexes using Me4-DTNE that has been obtained in a more simple synthetic procedure, with preferably without needing to distil Me4-DTNE prior complexation.